By John Darnton

Dutton. 421 pp. $24.95

By Sally Squires, a staff writer for the Health section of The Post.

Ever since Scottish scientist Ian Wilmut announced that he and his colleagues had successfully cloned a sheep named Dolly, there has been wide speculation about one day cloning humans. The technology to clone a human does not yet exist. But what if it did? And what if a group of unethical scientists were already ahead of the pack, cloning people to provide a cache of unlimited, perfect organs for a few wealthy movers and shakers?

Such is the premise of "The Experiment" by John Darnton, a medical thriller that catapults some of the most dire possibilities of cloning into today's world. Ever since Mary Shelley created Frankenstein, the notion of an evil, mad scientist trying to play God has been a common theme of medical thrillers. As one best-selling author of this genre once confided during an interview, the secret is to take a classic and spin it into a new tale with a modern medical twist.

Darnton seems to have gravitated to that formula. "The Experiment" centers on a very real medical problem: the desperate shortage of organs. There are an estimated 80,000 candidates for organ transplants in the United States, and more than 4,000 people die every year while waiting for a new liver, kidney, heart or lungs.

In "The Experiment," a scientific cult led by a mysterious Dr. Rincon discovers how to clone people and promptly withdraws from society, hoarding the information for its own nefarious purposes. Bankrolled by a secretive, eccentric billionaire, the group sets up a cloning facility on a remote island off the coast of Georgia. The clones of the scientists and their children are called Jimminies--a bastardization of the word Gemini or twins--and are raised like fatted calves by Elder Physicians, who impose strict rules about good nutrition, regular exercise, no sex and, of course, no contact with the outside world. The Jimminies live in Spartan barracks and learn Rincon's Laws, in which science is God. Researchers alter DNA, insert new genes and try to achieve a kind of immortality for them and their families using the perfect spare parts of the clones when something goes wrong.

The tale begins when two Jimminies--twenty-somethings Skyler and Julia--discover the gutted remains of Patrick, a fellow clone. Patrick's heart was "harvested." Since it isn't the first time that one of the Jimminies has turned up dead, Skyler and Julia correctly deduce that their time is probably coming, although they don't know why. They have never left their tiny island, and there seems little that they can do to prevent the inevitable.

Enter Jude Harley, an aggressive young reporter for a Manhattan tabloid called the Mirror. Harley is assigned to cover a murder in Upstate New York. The victim has been executed with a single shot to the back of the head and his face and fingerprints have been methodically removed, along with a single small piece of skin from the inside of one thigh.

When Harley's story on the murder gets bumped to the back of the Mirror by a juicier murder, committed by a twin, he's assigned to do a sidebar on what makes twins tick. He meets Tizzie Tierney, a dazzling young researcher at Rockefeller University, who tutors him on the various aspects of twin research. Identical twins have the same genetic code, making those separated at birth the ideal candidates to explore the age-old question of nature vs. nurture.

A romance quickly develops between Tierney and Harley. But there's something missing in the relationship--Harley detects a troubling distance. Only when a series of events deposits Skyler on his New York doorstep does Harley begin to unravel the mystery that links him and Tierney with the Jimminies. In his quest, he solves the strange murder (including why the victim's identity was covered up), uncovers a conspiracy that stretches high into the ranks of the FBI and learns some painful truths about himself and his family.

Darnton, who is the cultural news editor of the New York Times and author of the best-selling "Neanderthal," is a facile writer, who weaves many twists and turns into the story and gets the science right. The beginning and end of "The Experiment" are fast-paced but the middle sometimes bogs down, and Darnton relies a bit too much on a deus ex machina to resolve his plot.

Still, "The Experiment" is an important, interesting and cautionary tale of what could happen to a society that lets scientists tinker too much. The amazing possibilities of genetics and gene therapy provide a vast new Pandora's box for the millennium. The questions, as "The Experiment" aptly illustrates, are how eager should we be to open it and what safeguards do we need before we peek inside?